There has been continuous progress in miniaturization and integration of a semiconductor integrated circuit formed on a semiconductor substrate. In order to achieve the miniaturization and integration, a substrate surface should be kept ultraclean. That is, organic compounds, metal, various particles, and oxides (oxide film) should be removed from the substrate surface and, for that purpose, substrate cleaning is carried out.
Conventionally, as a cleaning method for the substrate surface, RCA cleaning described in Non-Patent Document 1 was predominantly used. However, since this RCA cleaning uses a large amount of a high-temperature and high-concentration chemical solution and comprises a very large number of steps, there are concerns about the productivity and cost and even about the influence on environment.
In view of this, there have been proposed various cleaning methods in place of the RCA cleaning. For example, Patent Document 1 proposes a cleaning method comprising a first step of carrying out cleaning with ultrapure water containing ozone, a second step of carrying out cleaning with a cleaning liquid containing hydrofluoric acid, ultrapure water, and a surfactant while applying vibration at a frequency of 500 kHz or more, a third step of carrying out cleaning with ultrapure water containing ozone, a fourth step of carrying out cleaning with a cleaning liquid containing hydrofluoric acid and ultrapure water for removing an oxide film, and a fifth step of carrying out cleaning with ultrapure water.
According to the cleaning method described in Patent Document 1, all the steps are carried out at room temperature and it is possible to carry out the cleaning with less number of steps than RCA.
This cleaning method can remove an organic compound and a part of metals in the first step and can remove particles, the metals, and an oxide film in the second step.
Thus, the necessary cleaning is completed through the first and second steps. However, since the surfactant used in the second step remains on a substrate surface, the cleaning with ultrapure water containing ozone should be carried out again in the third step.
The surfactant can be removed by the cleaning with ozone-containing ultrapure water, but it is to be noted that an oxide film is formed on the surface. In order to remove this oxide film, the cleaning with the cleaning liquid containing hydrofluoric acid and ultrapure water is carried out and then the final cleaning with ultrapure water is carried out.
As described above, the cleaning method of Patent Document 1 has the problem that the superfluous step of cleaning is necessary by using ultrapure water so as to further clean new contamination resulting from the cleaning.
On the other hand, the inventors of this application have previously proposed, in Patent Document 2, a method for treating a semiconductor substrate with an aqueous solution containing alcohol (e.g. 2-propanol) and ketone and then removing the alcohol and ketone adhering to a semiconductor surface. The present inventors have made it clear that, by the treatment with the aqueous solution containing alcohol as described above, it is possible to suppress a dissolution amount of semiconductor atoms into the treatment solution and, as a result, the surface with a small surface roughness can be obtained. Further, the present inventors have also proposed to remove the alcohol adhering to the semiconductor surface by a treatment with xenon gas plasma.